Which of the following reactions is used to prepare Haloarenes?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Sandmeyer reaction
Haloarenes (aryl halides) are prepared mainly in two ways: by electrophilic substitution of arenes with chlorine or bromine and a Lewis acid catalyst, and from diazonium salts. In the Sandmeyer reaction a primary aromatic amine is diazotised with \( \ce{NaNO2} \) and a mineral acid in the cold, and the diazonium group is then replaced by –Cl or –Br with cuprous chloride or cuprous bromide:
\( \displaystyle \ce{C6H5NH2} \xrightarrow[\text{273-278 K}]{\ce{NaNO2} + \ce{HCl}} \ce{C6H5N2+Cl-} \)
\( \displaystyle \ce{C6H5N2+Cl-} \xrightarrow{\ce{Cu2Cl2}/\ce{HCl}} \ce{C6H5Cl + N2 ^} \)
So the reaction used to prepare haloarenes is the Sandmeyer reaction.
Why the other options are incorrect
Option (1) Stephen reaction — Incorrect. It reduces a nitrile to an aldehyde: \( \ce{RCN} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{SnCl2} + \ce{HCl}} \ce{RCHO} \).
Option (2) Gatterman-Koch reaction — Incorrect. It makes benzaldehyde from benzene with CO and HCl in the presence of anhydrous \( \ce{AlCl3} \)/CuCl:
\( \displaystyle \ce{C6H6 + CO} \xrightarrow{\ce{HCl},\ \text{anhyd. }\ce{AlCl3}/\ce{CuCl}} \ce{C6H5CHO} \)
Option (3) Cannizzaro reaction — Incorrect. It is the disproportionation of an aldehyde without \( \alpha \)-hydrogen by concentrated alkali into an alcohol and a carboxylate, e.g. \( \ce{2HCHO + NaOH -> CH3OH + HCOONa} \).
NCERT (2026-27 edition):
From Amines by Sandmeyer’s Reaction
